This invention relates to the vapor phase production of dialkyl carbonates from alkanols, oxygen, and carbon monoxide.
Dialkyl carbonates, particularly dimethyl carbonate, are valuable commercial products finding utility as solvents and as precursors to polycarbonates and isocyanates. Dimethyl carbonate is also useful as a gasoline fuel additive.
U.S. Pat. No. 5,004,827 discloses a process of preparing dialkyl carbonates involving contacting carbon monoxide, oxygen and an alkanol in the vapor phase in the presence of a heterogeneous catalyst comprising cupric halide or a mixed cupric halide alkali metal halide supported on a suitable support, such as activated carbon. Disadvantageously, the productivity of the catalyst is low, and the catalyst lifetime is short. More disadvantageously, the carbon support is combustible. As a further disadvantage, the carbon support contributes to catalyst attrition. An attrition resistant catalyst is desirable for vapor phase processes, regardless of whether the process is conducted in a fixed, transport or fluidized bed reactor.
U.S. Pat. No. 4,625,044 discloses a process of preparing dialkyl carbonates involving contacting carbon monoxide, oxygen and an alcohol in the vapor phase and passing them over a catalytic amount of a copper coordination compound supported on activated carbon. The coordination compound comprises a nitrogen-containing organic compound copper hydrocarbyloxy halide, such as, pyridine copper methoxy chloride. Disadvantageously, the productivity of the catalyst is low. Moreover, the carbon support is combustible and contributes to catalyst attrition.
U.S. Pat. No. 4,785,130 teaches a process of preparing organic carbonates involving contacting an alcohol, such as methanol, and carbon monoxide in the presence of a catalyst containing copper hydrocarbonoxy halide, such as copper methoxy chloride, and a quaternary ammonium halide, such as benzyltriethylammonium chloride. Disadvantageously, this process is conducted in the liquid phase. Liquid phase reactions are oftentimes unattractive due to the corrosiveness of the reactants, products, or catalyst system. As a further disadvantage, this process is not truly catalytic. Moreover, recovery of the catalyst from the liquid phase is costly.
Japanese Patent Kokai No. H2-256,651 discloses the production of carbonic acid esters by reacting an alcohol with carbon monoxide and oxygen in the vapor phase in the presence of metallic copper, optionally supported on a support material. The catalyst is taught to be obtained by first adding a solid support material to a solution comprising a copper salt, such as a copper carboxylate, dissolved in water or an organic solvent. The resulting material is reduced and heat treated. Disadvantageously, the productivity of this catalyst is also low.
European Patent application 0,534,545 discloses a process for the production of dialkyl carbonates in which the catalyst is regenerated continuously. The process comprises contacting in the liquid phase an alcohol, carbon monoxide, and oxygen in the presence of cuprous chloride and hydrochloric acid. Disadvantageously, this process requires enameled reactors, because hydrochloric acid is corrosive.
It would be desirable to find an effective catalytic process for the production of dialkyl carbonates, such as dimethyl carbonate, wherein the productivity of the catalyst is high and the lifetime of the catalyst is long. It would be desirable if the process was conducted in the vapor phase, since that would eliminate problems associated with liquid phase processes. It would be more desirable if the process employed a heterogeneous catalyst which would eliminate the problems of catalyst recovery. It would be even more desirable if the catalyst used a support other than carbon, such as alumina or silica, because an inorganic support would reduce the problem of combustibility and minimize losses through attrition.